This invention relates to a magnetic head suitable for high density magnetic recording, and particularly to a magnetic head using an amorphous magnetic alloy film having such distinguished characteristics as a high saturation flux density, a high crystallization temperature, a low magnetostriction constant and a high oxidation resistance.
As a result of recent remarkable progress of higher density and higher performance magnetic recording, higher coercive force tapes have been employed in the field of VTR (video tape recorders) to improve the recording density, and a need for magnetic heads using a magnetic material having a higher saturation flux density and a higher property has been increasing. Furthermore, as a result of higher density recording in the field of thin film heads for computer disks, there has been a need for making thin film magnetic poles to improve the resolution. However, magnetic saturation is liable to take place at the tip end of the thin magnetic pole, and thus there has been a need for a thin film magnetic head using a higher saturation flux density and higher performance magnetic film. Still furthermore, in the field of single pole type head for perpendicular magnetic recording now under extensive research, there has been a need for making the thickness of main magnetic pole extremely thin to improve the recording density. Thus, magnetic saturation is likewise liable to take place at the tip end of the magnetic pole, and consequently there has been a need for a single pole type head for a perpendicular magnetic head using a magnetic film having a higher saturation flux density and a higher performance to solve this problem. Still furthermore in the field of magnetoresistive heads for computer magnetic tape memory units, etc., there has been a need for a higher performance magnetic film as a shield thin film for such heads.
As a magnetic film for these magnetic heads, Ni-Fe based alloy films (permalloy films) have been so far mainly used, but recently sputtered amorphous films are now under development as magnetic films having a higher saturation flux density and a higher performance. Among them, particularly an amorphous alloy containing Zr as the main glass-forming element has a better heat resistance and a better corrosion resistance than amorphous alloys containing metalloid elements such as B, Si, P, etc. as the main glassforming element, and thus has distinguished characteristics for a magnetic film for the magnetic head. The Zr-based amorphous alloy can be specifically represented by such a composition formula as M.sub.a T.sub.b Zr.sub.c, where M is at least one of Co, Fe, Ni, etc. having a magnetic moment, and T is other transition metal element than M and Zr. The amorphous alloys containing Zr as the main glass-forming element are disclosed in Japanese Patent Application Kokai (Laid-open) No. 55-138049, Japanese Patent Application Kokai (Laid-open) No. 56-84439, etc. Among the Zr-based amorphous alloys, the Co-Zr based amorphous alloy, i.e., where M is Co, is a good magnetic material having a high magnetic flux density, but has a relatively high magnetostriction constant such as 2-4.times.10.sup.-6. By using such elements as V, Nb, T, Cr, Mo, W, etc. making a negative contribution to the magnetostriction coefficient of the amorphous alloy as the additive element T, amorphous alloys having a substantially zero magnetostriction constant can be obtained. Among the additive elements T, Nb and Ta have a relatively high ability to form an amorphous state, and thus amorphous alloy containing these element species has a broader range for the amorphous composition. That is, a high saturation flux density can be obtained therefrom.
As described above, the amorphous alloy represented by the composition formula M.sub.a T.sub.b Zr.sub.c has a high saturation flux density, distinguished corrosion resistance and thermal stability, and a substantially zero magnetostriction constant, and thus can serve as quite a suitable amorphous alloy film for the magnetic head. However, there are still the following problems in its application to the magnetic head. That is, the essential element for forming an amorphous state in the said amorphous alloy, i.e. Zr, is readily susceptible to oxidation. The value of the free energy change resulting from formation of an oxide of Co, the main component of the amorphous alloy, amounts to -43 to -47 Kcal per atomic weight of Co at 500.degree. C., whereas that of Zr is -230 Kcal, i.e. a very negative value. The more negative the value of free energy change of an element, the more oxidizable the element. Furthermore, the additional element T for the magnetostriction adjustment is generally more oxidizable than Co. For example, the value of free energy change of V is -145 Kcal, that of Nb is -188 Kcal, that of Ta is -186 Kcal, that of Cr is -112 Kcal, that of Mo is -134 Kcal, and that of W is -105 Kcal. In the amorphous alloy represented by the composition formula M.sub.a T.sub.b Zr.sub.c, the elements shown by T and Zr are so oxidizable that amorphous alloys comprising these elements are readily oxidizable. Even if thin films are prepared from these amorphous alloys either in vacuum or in an inert gas atmosphere according to a splat cooling method, the alloys are readily oxidizable by oxygen in the atmosphere, or react with a nozzle material composed of oxides to cause nozzle clogging. That is, the Zr-containing amorphous alloys are suitable for preparing films in high vacuum or a high purity inert gas atmosphere according to a sputtering method, etc.
The Zr-containing amorphous alloy films can be prepared by a thin film-forming technique such as sputtering, etc., but there are still the following problems in their application to a magnetic head. A process for preparing a magnetic head where a magnetic film is used in a magnetic circuit generally includes a heating step at an elevated temperature, for example, 150.degree. C. at the lowest and about 500.degree. C. at the highest. In the heating step, the Zr-containing amorphous alloy film undergoes surface oxidation, resulting in deterioration of the magnetic characteristics. Furthermore, these amorphous alloy films are often formed on a substrate of glass or oxides such as SiO.sub.2, ferrite, etc., or through contact with glass, oxides such as SiO.sub.2, ferrite, etc., or oxygen-containing organic materials such as resin, etc. on these amorphous alloy films. Thus, the Zr-containing amorphous alloys react with these oxides or oxygen in the resin to deteriorate the magnetic characteristics of the amorphous alloy films. The problems are remarkable particularly in the case of small film thickness, for example, in the case of a single pole type head for a perpendicular magnetic head using a magnetic film having a thickness of about 0.2 .mu.m as the main magnetic pole film, or a thin film magnetic head using a magnetic film having a thickness of about 1 .mu.m as a magnetic pole, or a magnetoresistive head using a thin film magnetic film as a magnetic shield film. Also in the VTR magnetic head using a magnetic head having a thickness of about 10 .mu.m, reaction takes place at the interface between the magnetic film and the glass or the oxide, and erosion of the magnetic film, deterioration of the magnetic characteristics, etc. occur. Thus, there still are the problems of deterioration of the magnetic head characteristics.